Experimental study of methane-oxygen premixed flame characteristics in non-adiabatic micro-reactors

In this paper, the effects of Reynolds number, geometrical parameters, and equivalence ratio on methane-oxygen premixed flame dynamics in non-adiabatic micro-reactors were investigated experimentally. The results showed that decreasing the inner diameter of the reactor could significantly influence flame operational regimes and propagation speed in the reactors in terms of suppressing hydrodynamic instabilities and compatibility with theory. In addition, the results showed that increasing the Reynolds number could shift the location of the maximum flame propagation speed in the reactors towards more fuel-lean mixtures. Therefore, it was considered that fuel-rich flames were more stable than fuel-lean ones. Moreover, two mechanisms of heat loss and flame instabilities were found to control flame propagation speed in small-scale reactors. In this regard, unlike the effect of heat loss mechanism on flame propagation speed, the instabilities on the flame surface and the consequent flame surface stretching could lead to a significantly higher flame propagation speed in the reactor than the free propagation flame speed. Meanwhile, it was shown that most established flames in reactors with 1 mm inner diameter were symmetric and more controllable. However, the flame shape in reactors with 2 mm inner diameter could be asymmetric under certain conditions.